1. Field of the Invention
The present invention relates to land mobile radio scanners and network delivery of audio received thereby. More particularly, the present invention is directed radio scanners operating as radio terminals that are interconnected by the Internet, and which announce availability of captured audio so that client terminals may request audio content through the Internet.
2. Description of the Related Art
Scanning radio receivers, commonly known as “police scanners” or simply “scanners”, allow users to listen to police, fire, aircraft, marine, business and other manner of one-way and two-way radio communications across a broad spectrum of frequencies, typically from 25 MHz to 1300 MHz, and including higher frequencies as well. These spectrum, broadcasting, and receiving systems, are generally referred to as Land Mobile Radio (LMR). Land mobile radio systems, also called public land mobile radio or private land mobile radio, is a term that denotes a wireless communications system intended for use by terrestrial users in vehicles (mobiles) or on foot (portables). Such systems are used by emergency first responder organizations, public works organizations, or companies with large vehicle fleets or numerous field staff. Scanners typically have a channel memory that is used to store one or more receiver frequencies, or indicia of frequency, which can be recalled by referencing a channel number, thereby simplifying the entry and selection of desired reception frequencies and reception channels. Various types of scanners are known, some operating in a few bands of frequencies with limited channel memory capacity, others being full-featured models that cover all the pertinent bands and including generous channel memory capacity. Scanners are enabled to sequentially change reception frequencies, thereby scanning through a list of frequencies, searching for broadcasts that may or may not be of interest to a user. In modern scanners the selection of a radio frequency generally includes specifying the radio frequency band and the receiver phase-locked loop (PLL) divisor that is requires to tune the receiver to discriminate the precise frequency of interest. Thus, the specification of the RF-band and PLL divisor with a digital selection means enables a precise reception frequency in most scanners.
Modern radio broadcast systems employ digital processors to control the allocation of frequencies for radio communications. This typically also includes spectrum utilization efficiency improving techniques that enable systems to offer a greater number of communications “channels” than the number of actual radio frequencies that may exist in a system. Thus, a single frequency may be utilized for a large number of channels, which are managed by a system protocol. The system protocols use various techniques for defining and allocating channels, and modern scanners have corresponding decoding systems or distinguishing channels from one another, as is appreciated by those skilled in the art.
Scanner radio receivers typically employ some form of squelch control so that noise and undesirable communications are not routed to a loudspeaker or other audio circuit. Carrier squelch can be used, which gates received audio to a loudspeaker based on the signal-to-noise ratio or carrier-to-noise ratio of the receiver demodulator output. Other systems employ out of band tones that are detected to control squelch. This is an example of a technique to provide more than one channel of communications on a single frequency. Certain receivers are sensitive to certain tones, and therefore receive and transmit communications only on channels where the tones match. One such system employs plural sub-audible tones, and is referred to as a continuously tone coded squelch system (“CTCSS”), as is well known in the art. The receiver checks for a particular one of the plural tones based on the channel programming, and detection of a matching tone enables the squelch gate of the receiver. Another system employs digital data fields that are broadcast along with the primary communication signals, and the receiver looks for a matching digital code. Such systems are referred to as digitally coded squelch systems (“DCS”). Other squelch control systems are known as well.
Early two-way radio systems employed a single radio frequency or a duplex pair of radio frequencies for two-way communications. Such systems lent themselves well to scanning receiver monitoring because a given two-way radio fleet of users, such as the local police department, could be readily monitored by receiving a single, predetermined, radio frequency. However, heavy radio use demand and congested airways caused manufacturers to develop more spectrally efficient radio systems. One solution was the trunked radio system where a group of two to twenty-eight duplex pairs of radio frequencies are allocated together for shared use by plural fleets of users. In a trunked system, talk group identities are assigned to the fleets, which are used to provide receiver squelch gate control for the plural members of any given fleet of users. The difference in a trunked radio system vis-à-vis a conventional system is that the radio frequencies are dynamically allocated during use. For each push-to-talk of a transmitter, the system dynamically allocates a radio frequency for the transmitter to use. As such, a conversation between a dispatcher and a fleet of patrol cars, for example, can change from frequency to frequency within the trunked group of frequencies during the course of a conversation. Thus, the conversation is carried out over an intermittent sequence of discrete radio transmission of audio content. Suppliers of scanning receivers addressed this difference in functionality by developing radios that could track the talk group identities (“talk group ID's”) and dynamically hop from frequency to frequency as the conversation progressed. The key to radio scanner operation in a trunking environment is to have all of the trunking frequencies for each trunk group stored in the scanner channel memory, typically associated with a system identity (“System ID”), and then track the talk group ID code of the desired fleet, along with the dynamic allocation of the trunking frequencies. In this way, the trunked scanner functions like a conventional scanner from the user's perspective, with the “channel” actually associated with both a trunking system ID and a talk group ID instead of the conventional radio system frequency-to-channel, plus squelch code, correlation. Certain trunking systems dedicate one of their allocated frequencies as a control channel carrying relatively high speed data signals, which are monitored by receivers looking for assignment to a talk channel from time to time.
Two-way mobile radio communications systems are widely used for a variety of applications including public safety, commercial, and personal communications. Radios with transmitter and receiver elements, commonly known as transceivers, participate in these communications. In addition, other radio receivers, such as scanners, monitor communications without participating through transmissions.
Most two-way radio communications operate according to a transmission trunked control system. This is different from the conversation trunked system. For example, a PSTN telephone call is conversation trunked in that the communications resource is set-up and maintained for the entire duration of a conversation, even during periods of quiet between the parties to the conversation. In a transmission trunked environment, the system operates in a push-to-talk mode. In this situation, each verbal statement from each user is individually transmitted. Each statement by a party to a conversation is transmitted on a radio frequency, and a conversation usually comprises a series of separate discrete transmissions with periods of quiet in which no radio signals occur between individual transmission signal elements. In some instances, if the gap between remarks is short, a transmitter may remain active with no gap in the carrier signal of the radio transmission between remarks. When used for conversation, the result is a radio channel with a series of separate discrete transmissions, each with a relatively short duration, typically in the range of two to sixty seconds. Depending on the level of activity on a channel, this may generate a regular patter of activity, or there may be inactive gaps extending to hours between conversations.
For the sake a clarity, the terms ‘channel’, ‘frequency’, ‘signal’ and ‘squelch’ are used as follows. The term ‘channel’ refers to a discrete communications path for the transmission of certain classes of related content that may be independently identified at a radio receiver, regardless of whether this path is currently active with the presence of a radio signal or inactive without the presence of a radio signal, such as a radio broadcast frequency, a coded squelch broadcast signal, or trunked radio system talk group ID. The term ‘frequency’ refers to an actual radio broadcast frequency on which a communications signal is modulated or may be modulated, such as a conventional frequency or a trunked system working channel. The term ‘signal’ refers to a discrete period of activity on a channel, such as a single radio transmission, or a series of closely spaced but discrete transmissions. In some cases, evident by context, ‘signal’ may refer to the content currently present on a broadcast frequency. The term ‘squelch’ refers to a test determining whether a signal is present on a particular frequency; squelch is true when there is no signal, and unsquelch is true when there is signal.
In common speech there may be confusion between these terms. For instance, in conventional radio systems, there is typically a one-to-one regional correspondence between channels and locally active broadcast frequencies. This encourages a perceived equivalence between the terms, or blurring of meanings. However, the terms have different technical meanings herein.
Frequency agile receivers, commonly known as “scanners”, are designed to receive signals on multiple communications channels by sequentially sampling (“scanning”) predetermined channels until an active signal is detected, and holding on that channel to receive audio until the transmission or series of transmissions is complete. The scanner then resumes the scanning process to detect the next new signal. Typical scanners can scan hundreds of channels. Since any individual channel will typically have long periods of inactivity, this technology is a practical way to monitor communications on multiple channels with a single receiver, although it is typically not plausible to receive simultaneous communications on different channels with a single receiver.
When a single receiver is receiving a transmission on one channel, it is typically insensitive to any radio communications on other channels. As a limited exception to that principle, some scanners have a ‘priority’ feature wherein the scanner periodically retunes to a designated “priority” frequency to test for signal, at the cost of brief gaps in the reception of the present non-priority signal. This tradeoff provides for greater reliability in coverage of signals on the designated priority frequency, at the direct cost of performance in the reception completeness of all non-priority signals.
With respect to prior teachings of record by the inventor of the present disclosure, a first co-pending U.S. patent application Ser. No. 11/600,476 to Sullivan et al. filed on Nov. 16, 2006, (hereinafter “Sullivan-1”) for a Network Audio Directory Server and Method, the contents of which are hereby incorporated by reference, was submitted by the inventors hereof. Sullivan-1 discloses a system and method of communicating audio through a network. Sullivan-1 addresses certain structure and techniques employed in the network environment. The method includes detecting audio content from an audio source by a first network terminal, sending a directory packet including a network address of the detected audio content to a second network terminal, and requesting the audio content through the network by the second audio terminal. The further step of storing the detected audio content in a buffer for audio packets identified by packet identities is added in some embodiments. The sending of a directory packet step may include sending a packet identity, and the requesting step may include specifying an audio packet according to the packet identity. A further step of sending a source packet including the network address of the detected audio content to a network directory server by the first network terminal may be added. Thusly, the directory server manages the requests and communication of audio content between feed source terminals and receiver terminals.
A first issued U.S. Pat. No. 8,125,988 issued on Feb. 28, 2012, Ser. No. 11/809,964, to Sullivan et al. filed on Jun. 4, 2007 (hereinafter “Sullivan-2”) for a Network Audio Terminal and Method, the contents of which are hereby incorporated by reference, was submitted by the inventors hereof. Sullivan-2 discloses network audio feed source terminals, receive terminals and methods. Sullivan-2 teaches a receive terminal that includes a network interface that receives network packets and a network packet scanner coupled to the network interface that sequentially scans received network packets in accordance with scan criteria. A content selector is coupled to the network packet scanner, and selects network packets containing units of audio content from the scanned network packets based on selection criteria. An audio content processor is coupled to the content selector, and processes the audio content in the selected network packets. The network packets may include directory packets containing audio content addresses, in which case, the content selector further selects directory packets based on selection criteria. An audio packet requestor is coupled to the content selector and the network interface, and operates to request audio packets through the network identified by the audio content addresses that correspond to the selected directory packets. Sullivan-2 also teaches a network audio feed source terminal, which is used for coupling units of audio content from an audio source to a network. The feed terminal includes a source interface that receives audio content from the audio source and a content monitor that identifies audio content in accordance with monitoring criteria. The feed terminal also includes a means for capturing a selected portion of the identified audio content as units of audio content in accordance with capture criteria, and, a network interface that couples the units of audio content into the network.
A second issued U.S. Pat. No. 8,429,287 issued on Apr. 23, 2013, Ser. No. 12/432,009, to Sullivan et al. was filed on Apr. 29, 2009 (hereinafter “Sullivan-3”) for a Network Audio Distribution System and Method, the contents of which are hereby incorporated by reference, was submitted by the inventors hereof. Sullivan-3 discloses audio content distribution from audio sources to client terminals through a network. An audio source interface receives raw audio from an audio source, and converts it into a digital audio clip in a digital audio packet, containing a timestamp and a channel identity corresponding to the audio source. A network audio server formats the digital audio packet into a network compliant digital audio file, which is stored at a network address. The network audio server generates a directory packet including the address of the digital audio file, the channel identity, and the timestamp, and, couples the directory packet to a directory server located on the network. The directory server outputs a directory stream to a client terminal on the network, which selects a directory packet and sends an audio file request through the network for the digital audio file. The audio file is then sent to the client terminal.
A second co-pending U.S. patent application Ser. No. 13/474,191 to Sullivan et al. filed on May 17, 2012 (hereinafter “Sullivan-4”) for Channel Monitoring with Plural Frequency Agile Receivers, the contents of which are hereby incorporated by reference, was submitted by the inventors hereof. Sullivan-4 discloses a system and method to efficiently use a plurality of ‘receivers’ to monitor a larger plurality of ‘sources’ for audio content. Upon identifying that a source is active, one of the plural receivers is assigned to convey the content to a destination. All other receivers are prevented from monitoring that specific source for the duration of its activity, but continue to monitor the remaining sources. ‘Source’ includes any source of information containing audio content. ‘Receiver’ includes any device capable of selectively conveying such content, including physical switches, hardware or software multiplexers, microphones, radio receivers, or any other means of obtaining such content.
The teachings of Sullivan-1, Sullivan-2, Sullivan-3, and Sullivan-4 encompass certain illustrative embodiments useful in a range of systems and methods for network audio content acquisition, delivery and reproduction. Generally, these teachings amount to building blocks that can be arranged to yield a wide variety of network audio delivery systems. However, the implementation of a network wide system for audio content distribution to a wide variety of end users presents numerous architectural and protocol challenges, particularly with respect to system access security, reliability and integrity, system growth, and traffic management. Thus, it can be appreciated that there is a need in the art for a system and method for implementing and managing a system of plural network coupled radio terminal sources for audio content and plural end user client terminals seeking access to such audio content.